This invention relates in general to a photovoltaic module and more specifically to a practical photovoltaic module which is protected from reverse bias damage caused by inoperativeness of one or more cells making up the module.
Photovoltaic modules are used for the generation of electrical energy upon exposure to illumination. The photovoltaic module comprises a plurality of individual cells connected together in a series string or in a combination series-parallel string. The particular combination of series or series-parallel and the number of cells included in the module depends upon the particular current-voltage requirements of the module.
Under nominal conditions, when a photovoltaic module is illuminated, each of the individual photovoltaic cells making up the module is forward biased. If one of the series connected photovoltaic cells is at least temporarily inoperative, however, it becomes susceptible to possibly serious permanent thermal damage if its available short circuit current becomes less than the current carried by the series string. Should this occur the cell may be forced into reverse bias under a voltage shock that can result in excessive localized power dissipation. Conditions leading to this potentially destructive situation can occur, for example, by a temporary shadowing of one or more of the cells in the string, or even of part of a cell.
Current design practice for protecting against such potential damage is to place a protective diode, poled to be reversed biased, across a string of 10-15 cells or across an entire module of 30-36 series connected cells. This protective diode arrangement, however, is often not sufficiently effective to prevent substantial module damage. In addition, even in those instances in which the protective diode provides adequate protection, the protective diode results in the waste of substantial amounts of module array power.
It is therefore an object of this invention to provide a photovoltaic module having improved protection against the inoperativeness of one or more cells making up the module.
It is a further object of this invention to provide an improved method of protecting solar energy modules.
It is yet another object of this invention to provide an improved photovoltaic module having improved protection against damage and without wasting substantial amounts of power.